Circuit breakers



Jan. 15, 1963 Filed Oct. 16. 1959 R. H. HILL ETAL CIRCUIT BREAKERS 5 Sheets-Sheet 1 Jan. 15, 1963 R. H. HILL ETAL 3,073,927

CIRCUIT BREAKERS Filed oct. 16. 1959 s sheets-sheet 2 1./ manA 9\ am- Fig. 7

Jan. l5, 1963 R. H. HILL ETAL 3,073,927

CIRCUIT BREAKERS Filed 00T.. 16. 1959 3 Sheets-Sheet 3 mien piene 3,ti73,92'7 CilfCUiT BREAKERS Robert H. Hill, South Beaver Township, Beaver County, Pa., and John C. Hetzler, ir., Laurel, Md., assigner-s to Westinghouse Electric Corporation, East Pittsburg-ii, Pa., a corporation of Pennsylvania Filed Get. 16, 1959, Ser. No. rgi 9 Claims. (Cl. 2nd- 88) This invention relates, generally, to circuit breakers and, more particularly to enclosed circuit breakers with automatic tripping means.

In a circuit breaker embodying a thermal time-delay and magnetic instantaneous tripping mechanism, it is important that the trip unit be free from tampering that could disturb the thermal and magnetic calibrations. The one-piece trip unit covers that have been used in the past have not sufficiently enclosed the tripping mechanisms to avoid possible tampering. This has been especially true wherein the tripping mechanism was adjustable from outside of the unit. If a trip unit cover were molded in one vpiece to completely enclose an adjustable tripping mechanism, it could not be assembled over the adjusting knobs which must protrude through the top of the cover.

' Accordingly, it is an object of this invention to provide f a circuit breaker embodying a safely enclosed automatic tripping mechanism.

Another object is to provide a circuit breaker embodying an automatic tripping mechanism with a base and a two-part interlocking cover cooperating with said base to safely enclose said tripping mechanism.

Another object is to provide a circuit breaker embodying an automatic tripping mechanism with a base and a two-part cover cooperating with said base to enclose said tripping mechanism wherein said tripping mechanism is adjustable from outside of said cover.

Another object of this invention is to provide a multipole circuit breaker having a completely insulated tie bar to insure against internal ashover between the poles of thebreaker.

Another object of this invention is to provide complete interpole barriers to insure against internal ashover on faults in a multi-pole circuit breaker.

Another object is to provide a multi-pole circuit breaker divided into compartments by a partition wall with an opening therein through which a movable tie bar passes,

wherein a barrier movable with the tie bar and a stationary L-shaped barrier cooperate to close said opening.

Another object is to provide a multi-pole circuit breaker embodying a stationary barrier that interlocks with a trip unit base and a partition wall to isolate the poles of the breaker.

Another object of this invention is to provide a circuit breaker including a housing with knockouts over the terminal connectors removable to provide easy accessibility for front connecting the terminal connectors to power conductors.

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation, together with additional advantages thereof, will be best understood from the following detailed description when read in conjunction with the accompanying (slarawngs.

In said drawings:

FIGURE 1 is a vertical sectional view of a panelboard mounted circuit breaker embodying the principal features of the invention;

FIG. 2 is a top plan view of the circuit breaker of FIG. 1, the panelboardplates being removed and part of the cover being broken away to more clearly illustrate the invention;

FIG. 3 is an enlarged elevational view of part of the trip device with the cover broken away to better show the device;

FIG. 4 is a sectional view on an enlarged scale of the trip device;

FIG. 5 is an enlarged perspective view of the two part interlocking trip unit cover;

FIG. 6 is an enlarged elevational view of the trip unit cover shown in FIG. 5;

FIG. 7 is an enlarged perspective View illustrating the interlocking stationary barrier; the movable barrier being shown in circular dot-dash lines; and

PIG. 8 is an enlarged perspective view illustrating an insulating end of the tie bar.

Referring to FIG. 1 of the drawings, the circuit breaker shown therein comprises, generally, a base 11 and a removable cover 13 both of which may be molded from a suitable insulating material. The breaker is of the threepole type, each pole being provided with a line terminal indicated generally at 15 and a load terminal indicated generally at 17 at opposite ends of the base 11.

The circuit breaker includes a stationary contact 21, a movable contact 23 and an arc extinguisher indicated generally at 25 for each pole. A common operating mechanism indicated generally at 27 is provided for simultaneously actuating the three movable contacts to open and closed positions. A trip device indicated generally at 29 serves to effect automatic opening of the breaker contacts in response to predetermined overload conditions in the circuit through any pole of the breaker.

The line terminal 15 is at the outer end of a conducting strip 31 which extends into the housing and rigidly supports the stationary contact 21. The movable contact 23 for each pole is mounted on a rigid contact arm 33 supported on a switch arm 35 secured to a tie bar 37 which extends across all ofthe poles of the breaker .and supports the switch arms for the several poles of the breaker for unitary movement to open and closed positions. The contact arm 33 is connected by means of a flexible conductor 39 to an intermediate or trip unit terminal 41 (FIG. 4) secured to the base 11 by a screw 42. 'Ihe trip unit terminal 41 is electrically integral with a looped heater element 43. A bimetal element 45 constituting a part of the trip device 29 is mounted on the other leg of the heater element 4? which is electrically integral with a load terminal conductor 44.

The operating mechanism 27 (FIG. l) is disposed in the center compartment of the housing and is supported by a pair of spaced frame members 53 (only one being shown) secured to the base 11. The operating mechanism comprises a pivoted forked operating lever 55, a toggle comprising toggle links 57 and 59, an overcenter spring means 61 and a pivoted releasable cradle 63 controlled by the trip device 29. An arcuate insulating shield 67 for substantially closing an opening 69 in the cover 13 is mounted on the end of the operating lever and has an integral handle portion 71 extending out through the opening 69 to permit manual operation of the breaker.

The toggle links 57 and S9 are pivotally connected together by a knee rpivot pin 73. The toggle link 57 is pivotally connected to the cradle 63 by a pin 75 and the toggle link 59 is pivotally connected to the switch arm 35 for the center pole by a pin 77. The overcenter spring means 61 is connected under tension between the knee pin 73 of the toggle 57, S9 and the outer end of the operating lever 55.

The circuit breaker is manually operated to the open position by movement of the handle 71 (FIG. 1) in a counter-clockwise direction to the oil position, which movement actuates the overcenter spring 61 to cause collapse of the toggle 57, 59 and opening movement of the magnet Vyoke.

"quired to instantaneously trip the breaker.

envase? g switcharms 35 for all of the poles of the breaker in a well-known manner.

The circuit breaker is manually closed by reverse movement of the handle 71 from the oif. to the on position which-movement causes the spring 61 to move overcenter and straighten the tog'gle'57, 59,the'reby"movingthe switch arms 35 for all of the poles to the closedposition.

In addition tothe bimet'al'elem'ent'45 (FIG. 4.)'the trip device includes a. series overload tripping ele'ctromagn'et 79 (FIGS. 3' and 4) for each'pole and a trip bar 81 common to all of the poles and biased to the Vlatching position by a' spring (not shown). The trip bar 'S1 is made of insulating materialand is pivotally 'supportedby means of pins 83 (only one being shown in FIG.'3) supported ina bracket 85 securedrto the base 11 bythe screw 42 for'the center pole of the breaker.

A latch 91 on the trip bar lnormally engages a latch mechanism,` indicated'generallyat 93, which, in turn, engages and releasably restrains the cradle 63 to releasably holdvthe operating mechanism in the closed position.

The tripping electromagnet indicated generally at 79 comprises a xed, laminated, vU-shaped magnet yoke 95, the laminations being secured togetherby rivets 94 (FIG. 3).l The magnet yoke 95 is supported by means of rivets 96 on a bracket 97 which is rigidly supported on an insulating base 98 for thetrip device. As is best seen in FIG. 2, the insulating base 98' divides thecircuit breaker housing longitudinally into two compartments, and serves to preventV passage of gases back into the tripping mechanism. A movable armature 99 (FIG. 3) is pivotally supported by vmeans of a knife-edge pivot 191 in a V-shaped notch l102 in the xed yoke 95. The armature 99 has a rod 103 pivotally connected thereto which, at .itsouter end, has a head y105 for engaging and operating the trip bar 81 upon energization of the magnet. Springs 107 are connected under ten-sion between inwardly extending ears 108 on the outer laminations of the armature 99 and in- Wardly extending ears 110 on the outer laminations of the The tripping magnet is energized bythe load -terminal conductor 44 which extends between the legs of the U-shap'ed magnet yoke 95.

lWhen a lowoverload currentoccurs, the bimetal element l45 ris heated, and when heated a predetermined amount, bends ltoward the left (FIG. 4) to engage the end of a calibrating screw 109 in the trip bar S1, and actuates fecting instantaneous release of the cradle 63. This effects automatic opening of the contacts for all of the poles of the breaker. l

It is necessary to reset and relatch the-breaker mechy anism following lan automatic opening operation before the contacts canbe closed. Resetting and relatching is effected by moving the handle 71 counterclockwise (FIG. l) as faras it will go. During this movement, a-projection 11.1 on the operating'lever '55 engagesashoulder on the cradle o3 and moves the latter in a counterclockwise direction. Near the end of this movement, the free or latching-end of the cradle 63 is reengaged with the latch mechanism 93 -in a well-known manner. The breaker contacts are then closed in the previously described manner by movement of the handle to the on7 position. Means are provided to Vselectively adjust within a predetermined range,`the minimum 'overload current re- This is accomplished by adjust-ing the position of the armature insulating trip-unit base 98 (FlG. 3).

relative to the magnet yoke to thereby vary the magnetic air gap.

The armature 99 is adjusted by means of a lever 119 (FIG. 3) which is controlled by a manually set cam 121. The lever 119 is pivotally mounted by a pivot pin 123 on the bracket 97 that is secured to the magnet yoke 95 and has a portion V127 extending upwardly therefrom. The lever 119 at one end is provided iwith a nose portion 129 which engagesa stepped cam surface 130 ofthe cam 121. The other end of the lever 119 is provided with a calibrating screw 135 which bears against the armature By turning the Calibrating screw 135, the calibration of the magnetic tr-ip may be set at the factory,..andy

the settingl ofthe screw135mayft-hen be sealed.

The upwardly extending portion 127 of thebracket I97 4) is bent over at.V right `angles asV at 141, and an adjusting knob 142 is rotatably mounted therein. A shaft 143 is keyed to the adjusting'knob 1,42 and rotates with it. vThe cam 121 is connected tothe bottomof the shaft 143. A slot 145l isprovided in the top ofthe knob 142 for receiving a screwdriver which is inserted ,to rotate the shaft 143 and vary 'the pos-itionofthe armature 99. When'the shaft 143 is rotated,` duetoV the yaction of the cam surface 139 on'the nose 129 ofthelever 1,'19(EIG. 3) the latter is Vpiv'otedabout its pivot 123causingthe Vadjusting screw .135 to'move the armature 99 andg thereby vary the distance between the armature andthe magnetic .yoke 95. [This 'tripping mechanism; is moreully described in a'patent application ,off Glen' R.' F[nomasl let al.,

anism to'prevent tampering onceV thecalibration has been` set. This is achieved by a two-,partinterlocking cover :that will prevent passage; into'the trip..unit,ofvr a -wire '1/32 of anv inch,or greater, in diameter.

vThe tripping mechanism is :supported on the ,molded A `molded .insulating cover (FIGS. 5,. and 6) comprising arbottomfpart-147 and a top part 14),.isjprovided` tocoope,ratev-with'the ,base 98.to.enclose the tripping mechanism. Iheparts 147 and 1`i-9Yformfavmainpanel "143l and 'fourpsidewalls "150.` There are three openings 151'in the ;top..side,wall

L15@ of the ,top part .149 to.,allOW passagefofthe, three adjusting knobs 142 (FIG. 4).r Twoopeningsf153. (FIGS. 5 and 6) are provided.on opposite .sides ,at the front .of the top part of. the main.- panel throughwhich screws (notshown) pass .to,engageinternally :threaded openings 155 k(onlyone vbeing shownin "FIG. 3),.in,the trip unitbase 98m ordertomount .thetop part149to the base 9S.

- The bottom part 147 of :the tripfunitcover, .has three notches l157 therein forallowing passage ofthethree `load terminal ,conductors 44,. .and,.three .notches .159

therein which t around a bottom loop 161 (FIG. 4.)y of -each of the .conductorsett Thebottom-,part.147711316 r bottom part .147 is set in place. rst `with ythe supporting trip-.unitfbase 98 firmly securingthetrip-unit.cover1147,

149 to the base 98. The supporting projections vv167 keep the lower part 147 from moving downwards and sidewardsfand the interlocking `portionslol, .165 keep the lower part Yfrom movingr out-wardsaand4 upwards-so that there is .no'need for anyl additional.mountingscrews to connect the lower part 147 to the trip-unit base98;

Another safety feature of this invention is the provision of a completely insulated tie bar to prevent flashover between the poles of the breaker. As was previously described, the tie bar 37 supports and moves all three of the movable contacts. Referring to FIG. 8, the tie bar 37 comprises a metal bar 171 having a square cross section, and an insulating cover 173 which extends out over the ends of the tie bar creating a pocket at each end. Each of these pockets is filled with a fluid composition 175 which is hardenable in place to insulate the ends of the tie bar, thereby preventing flashover between the ends of the bar and the outer poles. This composition may be either a wax or an epoxy resin, but preferably is a glycidyl polyether of a polyhydric phenol having a 1,2-epoxy equivalency between l and 2. The preferred composition has a high dielectric strength, and is particularly suitable for this application because it is adapted to be cured hornogeneously to a solid state without undergoing substantial volume shrinkage. The preferred composit-ion is more specically described and claimed in Patent No. 2,768,992 to Florian J. Zukas, and assigned to the assignee of the instant application.

Another safety feature of this invention is the provision of improved means for isolating the poles in the multi-pole circuit breaker. As is shown in FIG. 2, the trip-unit base 98 extends transversely across the breaker dividing it longitudinally into two portions. There are two partition walls dividing the portion to the right into three compartments, each of which houses the contacts for'one pole of the breaker. As is'illustrated in FIG. 7, each of the partition walls 179 comprises a top part 179a that is molded integral with the cover A13, and has a slot 180 that interlocks with an insulating projection 181 on a bottom part 179k which bottom part is molded integral with the casing base 11. There is an opening in the bottom part 179b through which the tie bar 37 passes. This opening is partially closed by a circular barrier 185 (shown in dot-dash lines in FIG. 7) that is attached to, and movable with, the tie bar 37. If the movable barrier 185 were large eno-ugh to completely close the opening in the partition wall, the trip-unit base 98 would restrict rotational movement'of this barrier. Therefore, a molded insulating stationary barrier 187, has'been provided to cooperate w1th the movable barrier 185 in order to completely close this opening. 1

The stationary barrier'187 is substantially L-shaped, and has a projection 189 extending around its outer edge. The projection 189 fits into a slot 191 in the trip-unit base, and into slots in the` bottom part 1791) and top part 179a of the partition wall. As can be seen in FIG.- 7, the stationary barrier 187 interlocks with the trip-unit base 98, and with the partition wall 179 when the parts are in place, and it cooperates with the movable barrier 185 to close the tie bar opening in the partition wall to prevent passage of gases between the poles of the breaker.

A further safety feature of this invention is the provision of knockouts 195 over the terminals 15 and 17 (FIGS. 1 and 2). In FIG. 1, the circuit breaker is shown In order to connect the breaker, the panelboard plates 197 and 199 are lifted and the breaker cover 13 is removed. A conductor 213 is placed Within the housing 205 over the conductor 44. A tool is then inserted into the opening 206 of the member 209, and rotated to move the pressure plate 207 down clamping the conductors 213 and 44 together. The connection at the load terminal 17 is termed a front connection.

The line terminal 15 is rear connected to a bus bar 2.15 by means of a conducting bus strap 217. With the panelboard plates 197 and 199 lifted and the casing cover 13 removed, an elongated screw 21S is passed through an opening in the conductor 31 and threaded into an opening in the bus strap 217. The bus strap 217 is connected to the bus bar 215 by a screw 219.

After the circuit breaker is connected, the cover 13 and panelboard plates 197 and 199 are attached in place as shown in FIG. l. Each of the terminals 17 and 15 is interchangeable for either a front connection or a rear connection. When the breaker is mounted in a panelboard, the knockouts 195 function as insulating means between the metallic panelboard plates 197 and the metallic terminal structure at 17; and between the metallic panelboard plate 199 and the metallic terminal structure at 15. It must be noted, however/that for this application, the cover 13 must be removed 'to provide access to the members 209 and 218.

When itis desired to use the circuit breaker outside of Vapanelboard, the knockouts y195 canbe removedv and a screw driver or other tool can be placed through the openings left thereby so that the terminals 17 and 15 can be connected without removingl the circuit breaker cover 13.` During use outside of a panelboard, there are no metallic panelboard plates 197 and 195 over the breaker so that there is no need for keeping the insulating knockouts in place.

From the foregoing description, it will be seen that the invention provides an improved, more dependable and safer circuit breaker. An adjustable tripping mechanism is supported' on an insulating base and is safely enclosed by a two-part interlocking cover. Air pockets, 'in the ends of the tie bar, are lledwitha fluid composition, hardenable in place, to insulate said ends. The opening in each partition wall, through which the tie bar extends, is closed by a movable insulating barrier attached tothe tie bar and an L-shaped insulating stationary barrier which interlocks with the partition wall and a -1 trip-unit base, and which cooperates with the movable Y minals.

barrier to isolate the compartments of the breaker. A further safety feature'is the provision of knockouts in the insulating cover of the breaker directly over the ter- When the circuit breaker is mounted in a panelboard, the knockouts are allowed to remain in place as it would be mounted in a panelboard in a manner well known in the art.

Metallic panelboard trim plates 197 `and 199 iit over the two ends of the breaker, the center portion of the breaker being open so that the operating handle 71 is accessible from outside of the panelboard. The plate V197 has a flange 201 that ts intoa slot 203 molded in the breaker cover 13. A pressure-type connector is provided at the load terminal 17 comprising a housing 205, a pressure plate 207 and a member 209 rotatably attached to the pressure plate 207. The member 209 is externally threaded, and iits through an internally threaded opening in the top of the housing 205. An internal hexagonal opening 206 (FIG. 2) is provided at the outer end of the member 209 for receiving a suitable tool for turning the member 209. The conductor 44 is attached to the inside base of the housing 205.

sav

providing insulation between the metallic terminal structures and the metallic panelboard plates. The breaker, in this instance, is known as having a dead-front. For a panelboard mounting, the breaker cover must be removed when the breaker is connected, so that a screw driver or other tool can be inserted to yfasten the terminal connections. When it is desired, however, to use the breaker outside of a panelboard, the insulating knockouts are removed permitting passage of a screw driver so that there is no need to remove the breaker cover in order to fasten the terminal connections.

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details 1. In a multi-pole circuit breaker, a plurality of stai tionary contacts and a plurality of movable contact between'said compartments.

structures cooperable therewith toopen and close lsaid circuit breaker, a rotatable tie bar for moving saidvmovable contact-structures, an operating mechanism for rotating .said tie bar, said tiebarcomprising a metallic bar and an insulating cover extending past the ends of Isaid metallic bar creating apocket at each end of said tie bar, 4and saidV pockets being illed witha iiuid composition hardenable in place to insulate said ends of said tie bar. 1 2. In a multipole circuit breaker, a plurality of stationary contacts vand a plurality of movable contact structures cooperable therewith to open and close said circuit breaker, a rotatable tie bar for moving said movable V.contact structures, an operating mechanism for rotating .said tie b ar, said tie bar comprising a metallic bar and an insulating cover extending past `the ends of said metallic bar creating a pocket at each end of said tie bar,

and said pockets being lled with a fluid wax composition hardenable in place to insulate said ends of said tie bar.

3. In a multi-pole circuit breaker, a plurality of stationary contactsand a plurality of movable contact structures cooperable therewith to open and close said circuit breaker, arotatable tie bar 'for moving said movable contact structures, an operating, mechanism for rotating said tie bar, said tie bar comprising a metallic bar andan insulating coverextending past the ends of said metallic barcreating a pocket at eachend of said tie bar, and said pockets being iilled with a hardenableiiuid insulating composition comprising a glycidyl polyether of Va polyhydric phenol having a l,2 epoxy equivalency between 1 and 2. f

4. In a multi-pole circuit breaker, an insulating housing, an insulating tripunit base dividing said housing longitudinally into a iirst part and a second part, at least one partition wall dividing said first part transversely into at least two compartments, saidlpartition wall having an opening therein, a movable tie bar extending through said 5. In a multi-.pole circuit breaker, aninsulating :hous- .ing, ansinsulating trip-unit base dividing said housing longitudinally into a first part and a second part, said housing comprising a base anda cover, at least one partivltion Ywall in said base,at least one partition wall in said Icovcr, said partition walls .interlocking to divide said first parrot said .housing transversely into at least two compartments, said base Y'partition wall having an opening therein, yalmovable tie ybar extending through said openf ing into each oisaid compartmentsan insulating barrier connected to said tie bar and movable therewith, an in- `:sulatingestationary barrier interlocking with said trip-unit f base said base partition wall and said cover partition wall, Yand said stationarybarrier cooperating with said movable barrier to close said opening to prevent passage of gases M 6. A circuit breaker comprisingrelatively movable con- .tacts and means releasable toeliect automatic opening of saidcontacts, trip means operable to eiectl release of said releasable means, said trip meanscomprising an energizing member, a magnet yoke structure disposed to be energized by said member, an4 armature movable'relative to said magnet Yyoke structure, adjusting V*means comprising an `adjusting knob operable to vary the position of said armature relative to said magnet yoke1structure, a trip means enclosure comprising a base and a cover mating with o u cover is in place said adjusting knob passingthrough said .opening to permit operation of said adjusting knob from outsidev of said trip means enclosure.

7. A circuit breaker comprising a pair of contacts and means releasable to eiect automatic opening of said contacts, trip means operable to eiiect release of said releas-4 able means, said trip means comprising an energizing winding, a magnet yoke disposed Vto be energized by said winding, an armature movable relative to said magnet yoke, adjusting means comprising a knob operable to vary tr e position of said armature relative to said magnet yoke, a trip means enclosure comprising a base and a cover cooperable with said base to enclose said trip means, said cover comprising two mating parts, when said parts are mated together said cover comprising a main panel and four'side walls extendingfrom said main panel, a first of said parts comprising one of said side walls which one said side wall has an opening therein, means fastening one of said parts to said base, said base and said one part cooperating to hold the other of said parts in posireleasable means, said trip means comprising an energizing winding, a magnet yoke disposed to be energized by said winding, an'armature movable relative to said magnet yoke, adjusting means including an adjusting knob operable to vary the position of said armature relative to said, magnet yoke, a trip rmeans enclosure comprising a base land a cover, said lcover comprising a iirst part and a second part, rwhen said parts are mated together said cover vcomprising a main panel and four side walls extending from vsaid main panel, said iirst part comprising one of said side walls which one side wall has an opening therein, means fastening said rst part to said base, when said rst part is fastened to said basesaid first part and said base cooperating to hold said second part in position to thereby 'enclose said trip means, when said first part isin place saidadjusting knob passing through said opening to permit operationfofsaid adjusting knob from outside of said tr1p means enclosure.

9. In a multi-pole circuit breaker, a plurality V,oi' staftionary contacts and a plurality of movable contact struc- 'tures cooperable'therewith to operi and close said circuit breaker, a rotatable tie barfor moving said movable contact structures, an operating mechanism for rotating'said tie bar, said' tie bar comprising a metallic bar and an insulating cover extending past the ends of said metallic bar creating a pocket at each end of sa1d t1e bar, and sa1d lpockets being filled with a lluid epoxy composition hardenable in place to insulate said endsof said tie bar.

said base,.said cover comprising two mating parts, when -said vparts are `mated together said cover comprising a main panel and four side walls extending from said, main panel, one of said parts comprising one of said 'side walls `whichone side wall has an opening therein, when said References Cited in the file of this patent `UNITED STATES PATENTS 1,955,327 Dorfman Apr. 17, 1934 1,996,891 Van Valkenburg Apr. 9, 1935 2,130,904 Sandin Sept. 20, 1938 2,204,409 Gano June l1, 1940 V2,265,030 l Dorfman Dec. 2, 1941 v2,491,959 Dyer Dec. 20, 1949 2,797,277 Dorfman June 25, 1957 2,797,278 Gelzheizer "June 25, 1957 12,863,969 Edmunds Dec. 9, 1958 2,897,327 v- De Smitt July 28, 1959 2,917,607 Sterling Dec. 15, 1959 v2,920,161 Dessert Jan. 5, 1960 2,937,251 Cellerini May 17, 1960 y2,961,811 Steven Apr. 24, 1961 

8. A CIRCUIT BREAKER COMPRISING RELATIVELY MOVABLE CONTACTS AND MEANS RELEASABLE TO EFFECT AUTOMATIC OPENING OF SAID CONTACTS, TRIP MEANS OPERABLE TO EFFECT RELEASE OF SAID RELEASABLE MEANS, SAID TRIP MEANS COMPRISING AN ENERGIZING WINDING, A MAGNET YOKE DISPOSED TO BE ENERGIZED BY SAID WINDING, AN ARMATURE MOVABLE RELATIVE TO SAID MAGNET YOKE, ADJUSTING MEANS INCLUDING AN ADJUSTING KNOB OPERABLE TO VARY THE POSITION OF SAID ARMATURE RELATIVE TO SAID MAGNET YOKE, A TRIP MEANS ENCLOSURE COMPRISING A BASE AND A COVER, SAID COVER COMPRISING A FIRST PART AND A SECOND PART, WHEN SAID PARTS ARE MATED TOGETHER SAID COVER COMPRISING A MAIN PANEL AND FOUR SIDE WALLS EXTENDING FROM SAID MAIN PANEL, SAID FIRST PART COMPRISING ONE OF SAID SIDE WALLS WHICH ONE SIDE WALL HAS AN OPENING THEREIN, MEANS FASTENING SAID FIRST PART TO SAID BASE, WHEN SAID FIRST 